Furnace for the production of unsaturated hydrocarbons



Jan. 31, 1961 F. F. A. BRACONIER ETAL FURNACE FOR THE PRODUCTION OF UNSATURATED HYDROCARBONS Filed June 7, 1957 I5 Sheets-Sheet 1 INVENTORS.

Jan. 31, 1961 F. F. A. ERACONIER ETAL 2,970,178

FURNACE FOR THE PRODUCTION OF UNSATURATED HYDROCARBONS Filed June 7, 1957 3 Sheets-Sheet 2 ATTORNEYS Filed June 7, 1957 Jan. 31, 1961 F. F. A. BRACONIER EIAL 2,970,178

FURNACE FOR THE PRODUCTION OF UNSATURATED HYDROCARBONS THEE.

3 Sheets-Sheet 3 United States Patent FURNACE FOR THE PRODUCTION OF UNSATURATED HYDROCARBONS Frederic Francois Albert Braconier, Plainevaux, and Jean Joseph Lambert Eugene Riga, Liege, Belgium, assignors to Societe Belge de lAzote et des Produits Chimiques du Marly, Liege, Belgium, a company of Belgium Filed June 7, 1957, Ser. No. 664,400 Claims priority, application Great Britain June 27, 1956 14 Claims. c1. 260--679) This invention relates to a furnace for the production of unsaturated hydrocarbons such as acetylene by the partial combustion of more saturated hydrocarbons.

It is known that such partial combustion may be efiected in a flame pyrolysis reaction, preferably by the action of oxygen. timately mixed with oxygen, the mixture is forced through a distributor, and the partial combustion and pyrolysis are effected in a reaction chamber, the reaction products being stabilized by quenching.

It is desirable to preheat the comburent i.e., the combustion supporting gas such as oxygen, and the hydrocarbon to as high a temperature as possible, so as to avoid an excess consumption of oxygen. Since the reaction is only of short duration, it is also important that thereactants should be intimately and homogeneously mixed at the entrance to the combustion or reaction chamber. In this way, the state of the reaction is equalized all across the combustion area of the reaction chamber, and the reaction period may be precisely adjusted by quenching, whilst eificiently stabilizing the gaseous combustion products.

In the known furnaces, the reactants are generally separately pre-heated, and then mixed in an expansion chamber having a large volume, so that a sufliciently intimate mixture may be obtained. This limits the pre-heating temperature to avoid pre-ignition of the reaction mixture or back-firing before its introduction into the reaction chamber. Alternatively, it is known to mix the reagents in the cold and to preheat the reaction mixture by causing it to flow at high linear speeds through tubular coils. These speeds are in the neighborhood of the speed of sound, and are in any case higher than the speed of propagation of the flame through the mixture at the maximum pre-heat temperature for the mixture. This method requires a high expenditure of energy to ensure the flow of reactants at these high speeds, and, due to the expansion at high speed of the gaseous mixture entering the combustion zone, it is difficu-lt precisely to determine the length of the reaction zone and the position at which the combustion products must be quenched. Furthermore, due to the very high turbulence, the reaction period cannot accurately be'regulated with precision and this is detrimental to the unsaturated hydrocarbon content and the desired yields.

According to the invention, there is provided a furnace for the production of unsaturated hydrocarbons such as acetylene, comprising separate inlet feed chambers for c omburent and hydrocarbon reactants and a plurality of mixing tubes of restricted cross-sectional area connecting one of the feed inlet chambers to the combustion chamber of the furnace and a plurality of ejector tubes or nozzles for feeding the other reactant or reactants from the other inlet chamber to the inlet ends of the mixing tubes so as to draw gases from the feed chamber into The gaseous or vaporized hydrocarbon is in-- said mixing tubes, the position and dimensions of each ejector tube outlet in relation to the inlet of the corresponding mixing tube being determined according to the desired proportions in which the reactants are to be mixed in said mixing tubes.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made to the accompanying drawings, in which:

Figure 1 shows diagrammatically an axial section' through part of a vertical furnace of the circular type.

"Figures 2 and 3 show similar axial cross-section through modified constructional forms of the furnace of Figure 1.

Figure 4 shows a partial cross section of the lower portion of the furnace of Figure l.

' Referring firstly to Figure 1, a furnace for the partial combustion of hydrocarbons, is shown as comprising a combustion chamber 9,mixing tubes 6, and inlet feed chambers 1 and 3 for separately receiving the reactants to be mixed. A plurality of ejector tubes 2 connect the feed chamber 1 to the inletends 5 of the mixing tubes, and extend through the feed chamber 3. The ejector tubes 2 are supported by a circular plate 14 which separates chambers 1 and 3, and is apertured at 15 to provide inlets for the tubes 2. The mixing tubes 6 are held between an apertured plate 16, forming a bottom wall for the feed chamber 3, and an apertured plate 7 forming the top of the reaction or combustion chamber 9. The wall 8 of the reaction chamber surrounds the nest of mixing tubes 6, so as to form a water jacket therefor, and extends into the feed chamber 3, where it supports a grid 4 around the ejector tubes 2. The feed chambers 1 and 3 are provided with inlets 17 and 18, the inlet 18 leading into the upper of the two compartments formed in the chamber 3 by the grid 4. The outlet nozzle 19 of each ejector tube 2 is externally shaped as a truncated cone, and extends partly into the corresponding inlet end 5 of a mixing tube 6.

The device just described may be operated as follows: one of the reactants, either comburent i.e., combustion supporter, or fuel, is pre-heated in known manner as by conventional gas preheating apparatus as indicated at 23 and 24, and is then led at 17 into the feed chamber 1, and forced through the tubes 2 into the inlet ends 5 of mixing tubes 6. The other reactant is fed at 18 into the upper part of the feed chamber 3 and is homogeneously distributed into the lower part of the feed chamber through and by means of the grid 4. The flow of gases from the nozzles 19 into the inlet ends 5 of mixing tubes 6 draws the gases from the feed chamber 3 by ejector action into the mixing tubes, so as to form an intimate reaction mixture. The homogeneous reaction mixture is then forced into the combustion chamber 9, in which the partial combustion of the hydrocarbon fuel is caused to take place.

, Referring now to Figure 2, the furnace comprises a third feed chamber Iii separated from the chamber 1 by an apertured plate 20 which supports an ejector tube 11 thirty-six as noted below in Example 2) where-the in ihto the feed chamber 10 and through the ejector tube ll'into one of the tubes 2. The effect of this partial or extra feed through the tube 11 is locally to enrich the reaction mixture emerging from the corresponding mixing tube 6 in comburent so as to create local hot points or pilot flames at a few of the tubes 6 (e.g., four outof Patented Jan. 31, 1961 creased proportion of comburent reactant assures maintaining a flame for igniting or stabilizing the combustion of adjacent streams of reactant mixture if necessary and which increase the average stability of the reaction zone all across the outlets of mixing tubes 6. Alternatively,'the tube 11 may be used for adding one or more hydrocarbons or comburents to the reaction mixture, so as to obtain a mixed reaction of partial combustion and pyrolysis.

Referring now to Figure. 3, theplate 20 is apertured to provide inlets 21 and 22 for an additional ejector tube 12 and a 'feed tube 13, respectively. The extra ejector tube 12 is supported by the plate 20' and extends through the feed chambers 1 and 3, and the plate 14 to the inlet of a mixing tube 6. The feed tube 13 is held between the .apertured plates 7 and 20 and extends through the plates 14 and 16 and the chambers 1 and 3.

The extra ejector tube 12 and the feed tube 13 are positioned at but a few of the mixing tubes 6 (e.g., 4 tubes 12 or 13 for 32 mixing tubes 6 as noted below in Example 2) and thus allow further quantities of comburent gas, secondary gas or hydrocarbon to be supplied to the reaction chamber 9, as required by the desired reaction conditions. Thus, the ejector tube 12 by-passes the feed chamber 1, but the gases in the tube 12 are mixed with the gases in the chamber 3 on entering the inlet 5 of the corresponding mixing tube 6, while the feed tube 13 feeds gases directly to the reaction chamber 9.

The plates 7, 14 and 16, the various ejector tubes, and the mixing tubes 6' may all be of metallic construction, the parts adjacent the reaction chamber being protected by the water jacket. The wall 8 of the reaction chamber 9- may be covered by a water screen for preventing the deposit of carbon or other degradation products on it.

The device just described allows the reactants homogeneously to be mixed and pre-heated at a high temperature (e.g., 750 C. as noted below) for distribution to the combustion chamber 9 and shortens the usual mixing time and reduces the space usually required for a conventional elongated mixing chamber preposed to combustion chamber 9. The conditions obtained by the use of this device lead to a high stability, to substantial homogeneity in any transverse portion across the combustion area of the reaction chamber and to efficient working of the combustion furnace which allows the most desirable zone for quenching the partial combustion accurately to be determined. The gaseous reactants are rapidly intermixed at the inlets 5 of the mixing tubes 6., in which tubes the mixing of the reactants is further equalized. Furthermore, the use of mixing tubes of restricted cross-section leads to low turbulence, even at high feed speeds, and thus minimizes possible backfiring in the feeding device.

Accordingly, the device of the present invention difiers both as to concept and results and as to structure and operation from those already known. In known furnaces a plurality of ejector tubes my be used for supplying one of the gaseous reactants, while the other reactant is supplied through annular spaces surrounding the ejector tubes, for example as shown in United States Patent 2,179,378. In such known device, the gaseous reactants come together in the combustion chamber without prior mixing, so that there is substantial turbulence detrimental to the stability of the flame. In order to avoid backfiring the gaseous reactants must be sent into the combustion chamber at high velocity and without being previously pre-heated to a high temperature, and this involves a substantial increase in the consumption of energy and of oxygen without the possibility of obtaining high yields of acetylene.

The. following examples are illustrative of the present invention as applied to theproduction of acetylene, but

igmust be understood that the invention is not limitede ea- Example 1 A furnace as shown in Figure 1 comprises thirty-six tubes 6 made of refractory steel, distributed in a plurality of concentric circles, each tpbe having an internal diameter of 11 millimetres anda length of 200 millimetres. Methane gas of 98% purity, pre-heated to 750 C., is supplied through conduit 18 at the rate of 220 cubic meters per hour measured at normal conditions at 0 C. and 760 millimetres of mercury. The gas spreads through the chamber 3 and is homogeneously distributed by a.

grid 4 at the top of the tubes 6. Oxygen of 98% purity,

also preheated to 750 C., is supplied through the conduit 17 at the rate of 130 normal cubic meters per hour. The oxygen passesfrom the chamber 1 through the tubes 2 and into the tubes 6. At the outlet, from the tubes 6, the homogeneous mixture of methane and oxygen is ignited in the chamber 9. The pyrolysis gas is quenched yielding 440 normal cubic meters per hour of pyrolysis gas calculated on the dry value, containing 9% by volume of acetylene.

The device according to the present invention also makes it possible to treat highly pre-heated gases without fear of spontaneous combustion, the only limit being the capacity of the pre-heaters used on an industrial basis.

Other types of furnaces comprising a conventional mixing chamber cannot be used to pre-heat thegases beyond about 500 C. without running the risk of pre ignition of the homogeneous mixture of reactants in the mixing chamber. consumption per ton of acetylene is in excess of 10% of methane and 16% of oxygen relating to the foregoing example where the reactants are pre-heated to 750 C.

Example 2 In order to increase the stability of the flame the re--. action mixture subjected to pyrolysis is locally enriched;

in oxygen in a furnace such as the one shown in Figure -2.-

This furnace comprises thirty-six tubes 6 to which.

methane of 98% purity is introduced through the cham-v ber 3 and the grid 4 at the rate of 220 normal cubic meters per hour, and oxygen of 98% purity is introducedv through the chamber 1 and the thirty-six tubes 2 at the rate of normal cubic meters per hour. A further quantity of oxygen is introduced through four tubes 11 at the rate of 14 normal cubic meters per hour. The

reactants are. pre-heated to 750 C. Thepyrolysis gas contains 9% by volume of acetylene calculated on the dry value. tional oxygen is introduced through four tubes 12 or 13 as shown in Figure 3 instead of through the four tubes 11 shown in Figure 2, similarly at the rate of 15 normal cubic meters per hour, but the main supply of oxygen at the rate of 115 normal cubic meters per hour is supplied through thirty-two tubes 2 into the tubes 6.

What is claimed is:

1. In a furnace for the production of unsaturatedhydrocarbons by partial combustion of a gaseous mixture of a gaseous hydrocarbon reactant and a comburent gas reactant, the combination which comprises a combustion and reaction chamber in said furnace for said partial combustion of said gaseous mixture therein, a substantial plurality of mixing tubes for introducing said In such circumstances the specific In a modification of this device, the addi-,.

simultaneously to all said mixing tubes for introduction therethrough into said combustion chamber, a second feed inlet chamber separate from said first chamber for supplying said comburent gaseous reactant for introduction into said combustion chamber through said mixing tubes, means includinga plurality of supply nozzles substantially equal in number to said plurality of said mixing tubes and in flow communication with said second inlet chamber for supplying said comburent gaseous reactant from said second chamber into said mixing tubes, said supply nozzles having discharge ends of restricted cross-section substantially less than the internal cross-section of said mixing tubes and with each discharge end positioned directly adjacent the upstream end of one of said mixing tubes for directing high-velocity jets of said comburent gaseous reactant from said second feed inlet chamber into said mixing tube and for simultaneously drawing a supply of said hydrocarbon gaseous hydrocarbon reactant from said first feed inlet chamber into said mixing tubes for admixture of said gaseous reactants in said tubes as said two reactants are introduced into said combustion chamber, the aggregate open cross sectional area of all said mixing tubes being substantially less than the open cross-sectional area of said combustion chamber, a third gaseous inlet chamber and a plurality of supplementary supply nozzles in flow communication therewith for supplying a comburent gaseous reactant from said third chamber into said combustion chamber, the number of said supplementary supply nozzles being substantially less than the number of said mixing tubes and of said supply nozzles from said second feed inlet chamber, and said supplementary supply nozzles being spaced substantially uniformly among said plurality of said mixing tubes for supplying said gaseous comburent reactant from said third feed inlet chamber at only spaced selected points across said combustion chamber.

2. In a furnace as in claim 1 in which said second feed inlet chamber is contiguously preposed in the line of flow of said gaseous reactants to said first feed inlet chamber and in which said supply nozzles leading from said second feed inlet chamber to said mixing tubes traverse the interior of said first feed inlet chamber.

3. In a furnace as in claim 1 in which said first inlet chamber is transversely subdivided by a perforated partition with the perforations thereof being positioned so that said supply nozzles extend therethrough in leading from said second feed inlet chamber to said mixing tubes, said perforations being larger than the outside dimension of said supply nozzles extending therethrough providing annular passages through said perforations in said partition around said supply nozzles, and which furnace includes means for supplying said hydrocarbon gaseous reactant to said first feed inlet chamber upstream of said perforated partition for flowing of said hydrocarbon gaseous reactant through said perforations around said supply nozzles to said mixing tubes.

4. In a furnace as in claim 1 in which said supplementary supply nozzles from said third feed inlet chamber are positioned to direct a stream of said gaseous comburent reactant from said chamber into selected ones of said supply nozzles leading from said second feed inlet chamber prior to the introduction of said jet from said second chamber nozzles into said mixing tubes.

5. In a furnace as in claim 1 in which said supplementary supply nozzles lead directly from said third feed inlet chamber to the inlet end of selected ones of said mixing tubes for introducing a jet of said gaseous comburent reactant from said third chamber into only said selected ones of said mixing tubes for admixture therein with said gaseous reactant from said first feed inlet chamber and substantially without admixture of said gaseous reactant from said second feed inlet chamber.

6. In a furnace as in claim 1 in which said supplementary supply nozzles lead directly from said third '6 feed inlet chamber into said combustion chamber for supplying thereto from said third inlet chamber at said selected spaced points said comburent gaseous reactant substantially without admixture with said gaseous reactants in either said first or said second inlet chambers.

7. In a furnace as recited in claim 1 in which all said feed inlet chambers are contiguously and sequentially preposed to both said plurality of mixing tubes and said combustion chamber in the line of flow of gaseous reactants toward said combustion chamber. 8. In a furnace as in claim 1 in which said restricted cross-sectional area of said discharge ends of said supply nozzles from said second inlet chamber into said mixing tubes is correlated with said diameter of said mixing tubes whereby said gaseous mixture of said gaseous hydrocarbon reactant and said comburent reactant as introduced into said combustion chamber through said mixing tubes is too rich in hydrocarbon reactant for complete combustion thereof.

9. A method for production of unsaturated hydrocarbons from a gaseous mixture of a gaseous hydrocarbon reactant and a comburent gas react-ant by pyrolysis thereof, which comprises the steps of separately preheating said hydrocarbon reactant and said comburent gas reactant to a temperature near but below the ignition temperature of said mixture thereof, separately conducting said pre-heated gases to separate supply zones, flowing said gaseous comburent reactant from one of said supply zones in a substantial plurality of separate highvelocity jet streams through the other of said gaseous reactants in said other supply zone for entraining and admixing said other gaseous reactant with said highvelocity streams, directing said plurality of high-velocity streams with said gaseous reactant entrained and admixed therein into and through an equal plurality of separate mixing conduits of restricted cross-section, establishing a pyrolysis flame reaction in said admixed gas streams upon the emergence thereof from said separate mixing conduits, controlling the velocity of said gas streams in said mixing conduits to be in excess of the upstream flame propagation velocity in said mixture preventing backfiring in said gaseous mixture, and expanding said gaseous mixture in the area of said pyrolysis flame reaction for reducing the linear velocity of said streams below the flame propagation velocity thereof upon emergence of said streams from said conduits.

10. A method for production of unsaturated hydrocarbons from a gaseous mixture of a gaseous hydrocarbon reactant and a comburent gas reactant by pyrolysis thereof, which comprises the steps separately preheating said gaseous reactants to a temperature near to but less than the combustion temperature of said mixture thereof, separately supplying said pre-heated gaseous reactants to a mixing zone, said gaseous comburent reactant being supplied 'as a high-velocity jet :stream to said mixing zone for entraining said other gaseous reactant in said stream for intimate admixture of said reactants in said mixing zone, controlling the flow of said admixed reactants at said mixing zone in a substantial plurality of separate gas streams of high velocity in excess of the upstream flame propagation velocity of said mixture, expanding said gaseous mixture upon emerging from said separate stream mixing zones to reduce the velocity thereof below the flame propagation velocity thereof, and establishing a partial combustion flame reaction in said expanded gases for said pyrolysis production of said unsaturated hydrocarbon.

ll. A method as in claim 10 in which said gaseous reactants are both pre-heated to a temperature substantially above 500 C.

12. A method as in claim 10 in which said gases are preheated to a temperature of about 750 C.

13. A method as in claim 10 in which an additional quantity of a comburent gaseous reactant is supplied to selected ones only of said plurality of gas streams prior References Cited in theifile of this patent UNITED STATES PATENTS Sachsse et'alL Mar. 3, 1953 Sachsse etgal .;Dec. 29, 1953 Lehrer May 6, 1958 Hale et al. Jan. 13, 1959 FOREIGN PATENTS- France Apr; 28, 1930 

1. IN A FURNACE FOR THE PRODUCTION OF UNSATURATED HYDROCARBONS BY PARTIAL COMBUSTION OF A GASEOUS MIXTURE OF A GASEOUS HYDROCARBON REACTANT AND A COMBURENT GAS REACTANT, THE COMBINATION WHICH COMPRISES A COMBUSTION AND REACTION CHAMBER IN SAID FURNACE FOR SAID PARTIAL COMBUSTION OF SAID GASEOUS MIXTURE THEREIN, A SUBSTANTIAL PLURALITY OF MIXING TUBES FOR INTRODUCING SAID GASEOUS MIXTURE INTO SAID GASEOUS MIXTURE THEREIN, A ING TUBES HAVING A SUBSTANTIALLY CONSTANT DIAMETER SUBSTANTIALLY LESS THAN THE LENGTH THEREOF AND BEING POSITIONED ADJACENT EACH OTHER IN A CLUSTER-LIKE ARRANGEMENT EXTENDING TRANSVERSELY ACROSS SAID COMBUSTION CHAMBER AND WITH THE AXES OF SAID MIXING TUBES SUBSTANTIALLY PARALLEL TO EACH OTHER AND TO THE AXIS OF SAID COMBUSTION CHAMBER, A FIRST FEED INLET CHAMBER PREPOSED TO SAID COMBUSTION CHAMBER AND TO SAID PLURALITY OF MIXING TUBES AND INDIRECT FLOW COMMUNICATION WITH SAID MIXING TUBES FOR SUPPLYING SAID GASEOUS HYDROCARBON REACTANT SIMULTANEOUSLY TO ALL SAID MIXING TUBES FOR INTRODUCTION THERETHROUGH INTO SAID COMBUSTION CHAMBER, A SECOND FEED INLET CHAMBER SEPARATE FROM SAID FIRST CHAMBER FOR SUPPLYING SAID COMBURENT GASEOUS REACTANT FOR INTRODUCTION INTO SAID COMBUSTION CHAMBER THROUGH SAID MIXING TUBES, MEANS INCLUDING A PLURALITY OF SAID SUBSTANTIALLY EQUAL IN NUMBER TO SAID PLURALITY OF SAID MIXING TUBES AND IN FLOW COMMUNICATION WITH SAID SECOND INLET CHAMBER FOR SUPPLYING SAID COMBURENT GASEOUS REACTANT FROM SAID SECOND CHAMBER INTO SAID MIXING TUBES,SAID SUPPLY NOZZLES HAVING DISCHARGE ENDS OF RESTRICTED CROSS-SECTION SUBSTANTIALLY LESS THAN THE INTERNAL CROSS-SECTION OF SAID MIXING TUBES AND WITH EACH DISCHARGE END POSITIONED DIRECTLY ADJACENT THE UPSTREAM END OF ONE OF SAID MIXING TUBES FOR DIRECTING HIGH-VELOCITY JETS OF SAID COMBURENT GASEOUS REACTANT FROM SAID SECOND FEED INLET CHAMBER INTO SAID MIXING TUBE AND FOR SIMULTANEOUSLY DRAWING A SUPPLY OF SAID HYDROCARBON GASEOUS HYDROCARBON REACTANT FROM SAID FIRST FEED INLET CHAMBER INTO SAID MIXING TUBES FOR ADMIXTURE OF SAID GASEOUS REACTANTS IN SAID TUBES AS SAID TWO REACTANTS ARE INTRODUCED INTO SAID COMBUSTION CHAMBER, THE AGGREGATE OPEN CROSS SECTIONAL AREA OF ALL SAID MIXING TUBES BEING SUBSTANTIALLY LESS THAN THE OPEN CROSS-SECTIONAL AREA OF SAID COMBUSTION CHAMBER, A THIRD GASEOUS INLET CHAMBER AND A PLURALITY OF SUPPLEMENTARY SUPPLY NOZZLES IN FLOW COMMUNICATION REACTANT FROM SAID THIRD CHAMBER INTO SAID GASEOUS REACTANT FROM SAID THIRD CHAMBER INTO SAID COMBUSTION CHAMBER, THE NUMBER OF SAID SUPPLEMENTARY
 10. A METHOD FOR PRODUCTION OF UNSATURATED HYDROCARBONS FROM A GASEOUS MIXTURE OF A GASEOUS HYDROCARBON REACTANT AND A COMBURENT GAS REACTANT BY PYUROLYSIS THEREOF, WHICH COMPRISES THE STEPS SEPARATELY PREHEATING SAID GASEOUS REACTANTS TO A TEMPERATURE NEAR TO BUT LESS THAN THE COMBUSTION TEMPERATURE NEAR TO THEREOF, SEPARATELY SUPPLYING SAID PRE-HEATED GASEOUS REACTANTS TO A MIXING ZONE, SAID GASEOUS COMBURENT REACTANT BEING SUPPLIED AS A HIGH-VELOCITY JET STREAM TO SAID MIXING ZONE FOR ENTRAINING SAID OTHER GASEOUS REACTANT IN SAID STREAM FOR INITIMATE ADMIXTURE OF SAID REACTANTS IN SAID MIXING ZONE, CONTROLLING THE FOLLOW OF SAID ADMIXED REACTANTS AT SAID MIXING ZONE IN A SUBSTANTIAL PLURALITY OF SEPARATE GAS STREAMS OF HIGH VELOCITY IN EXCESS OF THE UPSTREAM FLAME PROPAGATION VELOCITY OF SAID MIXTURE,EXPANDING SAID GASEOUS MIXTURE UOPN EMERGINH FROM SAID SEPARATE STREAM MIXING ZONES TO REDUCE THE VELOCITY THEREOF BELOW THE FLAME PROPAGATION VELOCITY THEREOF, AND ESTABLISHING A PARTIAL COMBUSTION FLAME REACTION IN SAID EXPANDED GASES FOR SAID PYROLYSIS PRODUCTION OF SAID UNSATURATED HYDROCARBON. 